A kinetic equation has been formulated with the Ginzburg-Landau expansion in order to analyze the ordering processes and the associated changes of microstructures in Cu_3Au-type (Ll_2)alloys. The Ll_2 unit-cell has four lattice points which are divided into alpha-and beta-sublattice sites. Since the numbers of alpha-and beta-sublattice sites are different from each other (1 and 3), Ll_2 has four phases depending on which lattice point is beta-site. A single order-parameter cannot describe the state of order including the phase, as far as it has a real number. In the present study, a vectorized order-parameter S=S (eta1, eta2, eta3, eta4) is introduced, following a Potts model. Each parameter, eta1, eta2, eta3, eta4, has a non-negative value. First, the energy coefficients in the kinetic equation were determined so that the equilibrium phase diagram for Cu-Pt was reproduced. The changes in microstructures associated with ordering were analyzed by performing compuersimulation using the k
… Moreinetic equation. Following results were obtained : (i) Around an antiphase boundary, the phase changes smoothly in the way that eta1 decreases and eta2 increases compensationally. (ii) At an antiphase boundary, there forms a narrow region of a zero-degree of order and of high concentration of Pt, which corresponds to a "wetting phenomenon." (iii) The profiles of order-parameters obatined by the present simulation agree well with those calculated by a cluster-variation method. (iv) The hairpin mechanism in the annihilation process of periodic antiphase boundaries was successfully reproduced by the simulation. (v) Other important behaviors of antiphase boundaries and changes in microstructure were analyzed with the present kinetic equation.(1)逆位相境界ではη^1がスムーズに減少し、η^2増加する事により位相が変化する様子が確かめられた。(2)逆位相境界近傍では規則度が0となる状態が発生し、そこでの組成は状態図での不規則領域の値になる。これは、逆位相境界に不規則相の出現(すなわち、wetting現象)に対応する。(3)今回の計算で求められた逆位相境界近傍の規則度の変化は、クラスター変分法で得られている結果とよく対応している。(4)周期的逆位相境界がヘヤピン機構によって消滅していく過程がうまく再現できた。(5)このほかにも、実験で観察された逆位相境界の挙動や相分解の様子を本速度式により再現することに成功した。さらに、周期的逆位相境界の形成をも再現できるように速度式の改良を試みている。 Less